Thermal runaway means an eventual self-reinforcing process in which the temperature of a battery cell or pack rises uncontrollably because of multiple internal factors.
Do sealed lead acid batteries have a thermal runaway effect?
The thermal runaway effect observed in sealed lead acid batteries is reviewed and reassessed as a means for understanding the effect at a more fundamental level.
Thermal events in lead-acid batteries during their operation play an important role; they affect not only the reaction rate of ongoing electrochemical reactions, but also the rate of discharge and self-discharge, length of service life and, in critical cases, can even cause a fatal failure of the battery, known as “thermal runaway.”
What causes thermal runaway in lead-acid batteries?
For thermal runaway to occur in vented lead-acid batteries, very high extremes of charging current and the resultant high temperature must be present. While this document only considers thermal runaway in VRLA AGM products many of the causes are also applicable to GEL types.
SLA batteries taken to high DoD can experience accelerated sulfation rates which in rare cases can lead to thermal runaway through excessive heat build up due to higher demand on an underperforming battery. Now that we have covered thermal runaway in SLA, you may be wondering about thermal runaway in lithium batteries.
Batteries that are reaching or have exceeded the service life are at a significantly elevated risk of Thermal Runaway. This is due to the inevitable rise of internal resistance and the deterioration of the internal materials exceeding the rated number of discharge/recharge cycles.
What happens if a battery swells during a thermal runaway event?
During a thermal runaway event, the battery will self-discharge its entire capacity in a matter of minutes! The by-product of discharging so fast is an excessive amount of heat – and all of that energy has to go somewhere. Most commonly, this presents itself as a swelled battery – the battery will bulge from all sides.